c - SDL_SetColorKey doesn't set the background transparent

Question

it comes down to this code:

SDL_Surface *smiley = SDL_LoadBMP("./images/smileys/normal_up.bmp");
printf("Transparation worked: %i\n", SDL_SetColorKey(smiley, SDL_SRCCOLORKEY, SDL_MapRGB(smiley->format, 255, 0, 255)));
SDL_BlitSurface(smiley, NULL, window, NULL);
SDL_Flip(window);

This is the image I used. Using SDL on Arch Linux.

Answer 1

在 SDL_SetColorKey() 调用之前的这些行使整个工作正常：

smiley->format->Amask = 0xFF000000;
smiley->format->Ashift = 24;

现在我可以使用具有 32 或 24 bpp VideoMode 的 .bmp 或 .jpg 文件，一切正常！不知道为什么，不知道它是如何工作的。